The present invention relates to gas discharge light-producing systems and methods and, more particularly, to low-voltage, low-current, non-thermionic (e.g., no heated filament) ballast-free energy-efficient light-producing systems and methods which are more efficient, less expensive, substantially free of RF emissions and which can use conventional industrial, commercial or home gas discharge lamps (fluorescent tubes of various shapes and sizes, high-intensity discharge lamps, sodium vapor lamps, mercury vapor lamps, neon signage tubes).
In most commercial and home-grade fluorescent lighting systems, the heart of the system is the ballast, which is an inductance or transformer device that boosts the incoming voltage to a higher voltage level to start the fluorescent tubes and then, once the fluorescent tubes are lit or ignited (gas ionized or discharged), reduces the voltage to a level for normal continuous lighting. Moreover, these prior systems often use transformer filament windings to heat the filaments to therefore provide thermionic emission for assisting in the ignition phase. Heated filaments vaporize and form black deposits at the end of each tube and limit tube life. The evaporation of the Tugnsten filament invades the mercury vapor limiting luminosity and tube life. Early ballasted fluorescent lighting systems are shown in FIGS. 1A and 1B. In FIG. 1A the ballast unit L is in series with filaments F and switch S, and in FIG. 1B, glow switch GS which opens after the filaments are heated to initiate a discharge.
Ballast transformers are often the most expensive part of commercial fluorescent lighting systems. There have been numerous past efforts to provide fluorescent lighting systems which do not use ballast transformers.
Electronic ballasts of the type shown in FIG. 1C are common in the art and are disclosed in International Rectifier Publication Application Notes AN-995, "Electronic Ballasts Using the Cost-Saving IR2155 Driver". In this circuit, two power switches Q1, Q2 are connected in a totem pole topology with the tube circuits consisting of an LC series resonant circuit with the lamp across one of the reactances. The switches are power MOSFETS driven to conduct alternately by windings on current transformer T. In this circuit, the primary winding is driven by current to the lamp circuit and operates at the resonant frequency of L and C. A starting pulse is provided by a starting circuit comprised of resistor R1 and capacitor C1 and DIAC D1 connected to one of the gates of one of the power switches. After oscillation is initiated, a high frequency square wave (30-80 kHz) excites the LC resonant circuit. The sinusoidal voltage across the reactance C is magnified by the Q at resonance and develops sufficient amplitude to strike the fluorescent lamp. In this system, the filaments of the lamp are connected in series with the series resonant circuit.
In the case of neon tubes as used in neon signage, conventional art uses high voltage (as a rule of thumb approximately 1000 volts per foot of sign) ballasted driver circuits which are inefficient, noisy, large, emit heat, require heavy high voltage insulation, are not usually dimmable).